1. Technical Field
The present invention relates to a technique for acquiring a display state of a memory type display.
2. Related Art
Information display devices called “electronic papers” or “electronic books” have been developed. Many of the information display devices have a memory type display. The term “memory type” as used herein refers to a characteristic that can maintain a display for a certain time even without power supply. As the memory type display, for example, an electrophoresis display (hereinafter referred to as “EPD”) has been known. JP-A-2007-08529 discloses an EPD that has a holding capacitor for holding data of pixels in order to speed up the rewriting of image. In addition, JP-A-58-023091, which relates not to an EPD but to a liquid crystal display, discloses to use a memory cell (latch circuit) instead of a capacitor.
Data once written into pixels are lost even when the display has the holding capacitor as in JP-A-2007-08529. That is, data are stored in the holding capacitor as charges, but the charges are gradually lost because even the holding capacitor cannot hold the charges for a long time. It is also conceivable to use the memory cell as in JP-A-58-023091. However, power is required for the memory cell to maintain data, and data are lost when the power is not supplied. Since an EPD is most advantageous in that it can maintain a display even without power supply, supplying power to the memory cell in order to maintain data is to eliminate the advantage of the EPD.
As described above, while the EPD can maintain a display even without power supply, data to be displayed are lost. This involves the following problem, for example. In the EPD, when power is not supplied for a long time, migrating particles move due to thermal motion or ambient electric field, resulting in a reduction in contrast. In this case, the same data must be prepared again to refresh a display. It is also conceivable to store display data to a non-volatile memory different from a display. However, it is difficult to configure the EPD to include a memory of large capacity corresponding to the number of pixels.